This invention relates generally to inflators such as for use in inflating inflatable restraint airbag cushions to provide impact protection to occupants of motor vehicles. More particularly, the invention relates to inflators which rely primarily on reaction of a combustible material for the production of an inflation gas and such as may provide an inflation gas output which is adaptive to factors such as one or more crash and occupant conditions.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an “airbag,” that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins being inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an “inflator.”
Various types of inflator devices have been disclosed in the art for the inflation of an airbag such as used in inflatable restraint systems. One type of known inflator device derives inflation gas from a combustible pyrotechnic gas generating material which, upon ignition, generates a quantity of gas sufficient to inflate the airbag.
In general, the burn rate for a gas generant composition can be represented by the equation (1), below:rb=k(P)n  (1)where,                rb=burn rate (linear)        k=constant        P=pressure        n=pressure exponent, where the pressure exponent is the slope of a linear regression line drawn through a log-log plot of burn rate versus pressure.As will be appreciated, the pressure exponent generally corresponds to the performance sensitivity of a respective gas generant material, with lower burn rate pressure exponents corresponding to gas generant materials which desirably exhibit corresponding lesser or reduced pressure sensitivity.        
Typical pyrotechnic-based inflator devices commonly include or incorporate certain component parts including, for example: a pressure vessel wherein the pyrotechnic gas generating material is burned; various filter or inflation medium treatment devices to properly condition the inflation medium prior to passage into the associated airbag cushion and a diffuser to assist in the proper directing of the inflation medium into the associated airbag cushion.
To date, sodium azide has been a commonly accepted and used gas generating material. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving handling, supply and disposal of such materials. Further, economic and design considerations have also resulted in a need and desire for alternatives to azide-based pyrotechnics and related gas generants. For example, interest in minimizing or at least reducing overall space requirements for inflatable restraint systems and particularly such requirements related to the inflator component of such systems has stimulated a quest for gas generant materials that provide relatively higher gas yields per unit volume as compared to typical or usual azide-based gas generants. Still further, automotive and airbag industry competition has generally lead to a desire for gas generant compositions that satisfy one or more conditions such as being composed of or utilizing less costly ingredients or materials and being amenable to processing via more efficient or less costly gas generant processing techniques.
As a result, the development and use of other suitable gas generant materials has been pursued. Through such efforts, various azide-free pyrotechnics have been developed for use in such inflator device applications including at least some that have or exhibit a relatively high burn rate pressure dependency, e.g., have a burn rate pressure exponent of 0.4 or more.
In view of possibly varying operating conditions and, in turn, possibly varying desired performance characteristics, there is a need and a desire to provide what has been termed an “adaptive” inflator device and a corresponding inflatable restraint system. With an adaptive inflator device, output parameters such as one or more of the quantity, supply, and rate of supply (e.g., mass flow rate) of inflation gas, for example, can be selectively and appropriately varied dependent on selected operating conditions such as ambient temperature, occupant presence, seat belt usage and rate of deceleration of the motor vehicle, for example.
While such adaptive systems are desirable, they typically require the inclusion of additional components as a part of the associated inflator device and such as may undesirably increase one or more of the size, cost and weight of the inflator device. For example, various proposed or currently available dual stage inflator devices appear based on the principal of packaging together two separate inflators. As a result, such inflator combinations commonly include two distinct pressure vessels, two sets of filter or inflation gas treatment components, one for the output of each of the pressure vessels, and two distinct diffusers, again one for the output of each of the pressure vessels. Thus, it has been difficult to provide an adaptive inflator which will satisfactorily meet the size, cost and weight limitations associated with modern vehicle design, particularly as it pertains to driver side applications.
Perhaps the simplest form of an adaptive inflation system is an inflation system which utilizes an inflator which provides two levels or stages of performance, e.g., commonly called or referred to as a “two-stage” or “dual stage” inflator. Those skilled in the art, however, appreciate that even a relatively simple two-stage inflator may require significantly sophisticated actuation and/or control systems, as compared to typical single stage inflators, in order to realize particularly desired adaptive performance capabilities.
In view of the above, there is a need and a demand for a combustible material-based adaptive performance inflator device of desirably simple design and construction. In particular, there is a need and a demand for such an adaptive performance inflator device which more freely permits the use of azide-free pyrotechnics, such as those that have or exhibit a relatively high burn rate pressure dependency, e.g., a burn rate pressure exponent of 0.4 or more. Further, there is a need and a demand for adaptive performance inflatable restraint assembly combinations that are conducive for use in conjunction with relatively simple control arrangements.
Still further, while current trends and developments have focused to a large extent on the development and incorporation of various adaptive performance restraint installations, a large proportion and number of earlier inflatable restraint installations made use of traditional inflatable restraint assemblies. Thus, there is a need and a demand for an adaptive performance inflatable restraint assembly combination such as may, if desired, be used in a retrofit fashion within various existing inflatable restraint installations.
Commonly assigned, U.S. Pat. No. 6,314,889 issued to Smith, the disclosure of which patent is hereby incorporated by reference herein and made a part hereof, has been developed, at least in part, in response to such needs and demands. This patent discloses an adaptive output pyrotechnic inflator device and control assembly combination wherein the inflator device includes a first chamber wherein a supply of a combustible gas generant material having a burn rate which is pressure dependent is burned to produce gas. The inflator device also includes an exit of adjustable cross sectional area in fluid communication with the first chamber and wherethrough at least a portion of the product gas can exit the inflator device. The control assembly is in operational control communication with the inflator device and provides a control signal to the inflator device to effect adjustment of the cross sectional area of the exit dependent on at least one chosen product gas output performance factor.
While such an inflator device and control assembly combination has been successful in overcoming, at least in part, some of the shortcomings of prior assemblies, further improvements and developments are desired and have been sought. In particular, there is a need and a demand for a toroidal-shaped adaptive output inflator which can successfully overcome or minimize some or all of the above-identified shortcoming or limitations.